Considerable research work has been conducted in the field of silver metal treatment of bacterial infections. A variety of silver coated nylon cloths and fibers have been investigated, such as disclosed in Deitch et al. (Mar. 1983), "Silver-Nylon" a New Antimicrobial Agent, "Antimicrobial Agents and Chemotherapy, pp. 356-359; Mackeen et al. (Jan. 1987), "Silver-Coated Nylon Fiber as an Antibacterial Agent," Antimicrobial Agents and Chemotherapy, pp. 93-99; Deitch et al. (1987), "Silver Nylon Cloth: In vitro and in vivo Evaluation of Antimicrobial Activity," J. Trauma 27(3).
In the last noted reference, the use of a weak direct current to increase the rate of release of silver ions was investigated to determine the impact of the increased presence of silver ions. This aspect has been further investigated by several groups as reported in Berger et al. (Feb. 1976), "Electrically Generated Silver Ions: Quantitative Effects on Bacterial and Mammalian Cells," Antimicrobial Agents and Chemotherapy, pp. 357-358; Berger et al. (Nov. 1976), "Antifungal Properties of Electrically Generated Metallic Ions," Antimicrobial Agents and Chemotherapy, pp. 856-860; Colmano et al. (1980), "Activation of Antibacterial Silver Coatings on Surgical Implants by Direct Current: Preliminary Studies in Rabbits," Am. J. Vet. Res. 41(6):964-966; Falcone et al. (Mar. 1986), "Inhibitory Effects of Electrically Activated Silver Material on Cutaneous Wound Bacteria, " Plastic and Reconstructive Surgery, 77(3):455-459.
The technique of applying a current to a silver coated dressing or purifying devices or medical devices are also disclosed in U.S. Pat. Nos. 4,291,125; 4,411,648 and published U.K. Patent Application 2,189,677. It is thus apparent that considerable work has been conducted in the field of supplying silver ions in the area of infection or microbial contamination to control and eliminate microbial growth. This concept has been extrapolated further into the field of water treatment, such as disclosed in U.S. Pat. No. 4,407,865 where sand or diatomaceous earth is coated with metallic silver to provide a sterilizing effect as the contaminated waters flow over the filtered material.
It is apparent that sources of silver ions for instance would be particularly useful in surgical and other types of wound dressings. This aspect has been investigated and reported in U.S. Pat. No. 3,800,792, Canadian Patent 1,212,879 and published U.K. Patent Application 2,134,791. Metallic silver is incorporated into the dressing in one form or another and through dissolution silver ions are released into the treated area. U.K. Patent Application 2,134,791 discloses that composites containing various metals, such as silver, gold, palladium, platinum and tin are useful in surgical dressings, where the preferred metal is silver. It is postulated that the slow release of silver ions is facilitated by a galvanic interaction with the moss; i.e., substrate, of the dressing with added metallic or nonmetallic compounds. However, this patent is silent on how galvanic interaction is developed and directed toward slow release of silver ions in this moss based dressing composition.
European Patent Application 0206024 discloses use of very smooth coatings of various metal combinations on medical devices, such as catheters to provide some antimicrobial activity when the devices are in contact with body fluids.
U.S. Pat. No. 4,418,686 and published U.K. Patent Application 2,194,155A are directed to an implant active in releasing silver ions to treat a bacterial infection. In U.S. Pat. No. 4,418,686, the implant consists of a plurality of spaced-apart metallic bands on a plastic insert where the surfaces of the bands consist of alternate materials, such as silver and gold. The presence of the silver and gold metals in the presence of body fluids results in a galvanic action which is intended to release or liberate silver ions. The implant is of a coiled construction and has metallic bands of considerable size. Such obtained macroscopic galvanic action is not effective, or suitable for most surgical dressings. U.S. Pat. No. 4,252,525 discloses a dental implant where spaced-apart bands of silver and gold are vacuum deposited onto the body of the implant. In addition to these metals, other suitable substances include aluminum, copper, zinc, alloys such as silver-zinc-allantoinate, and silver sufadiazine, for release of metal ions in providing bactericidal and germicidal action. Other types of implants, which have been treated with silver ions, include catheters which are marketed by Baxter Travenol Laboratories under the trade mark AgX.
The prior techniques involving the use of metal ions in treating microbial infections do not provide a sustained enhanced release of antimicrobial substances. Most existing devices are for short-term applications or suffer from the drawback of very slow release of material. The elements of interest are in fact among the most stable elements. They do not readily dissolve at significant rates on their own, and when in contact with most other metals, will cause such others preferential release. Even when in contact with nobler metals, the differences on the electrochemical scale are quite small that galvanic action occurring over macroscopic areas of contact does not significantly enhance the release of ions to the level needed.
It is appreciated that the release of metal ions may be expedited by the application of external electric current. However, in many applications, such as in normal bandages or implants, this is practically impossible.
A variety of materials are used every day in treating or preventing infections in humans, animals and the like. For example, catheters, sutures surgical gloves, implants, bandages, diapers, diaper liners, dressings, small adhesive dressings, sanitary napkins and insoles are just a few. Normally, bandages are used as a barrier to airborne pathogenic organisms infecting a cut or wound. However, once infection occurs, the bandage is no longer of any benefit. If the bandage were provided with a broad spectrum antimicrobial agent, on the portion of the bandage which is in contact with the wound and surrounding skin, the bandage becomes an actively rather than a passively antimicrobial surface or microbial barrier. Catheters, implants, bandages, dressings and other materials, such as above, are used extensively every day by millions of people. As a result, any form of antimicrobial material incorporated into these types of devices must be safe for general unsupervised use, should avoid selection of resistant strains, and should be cost effective. Furthermore, the materials may have to retain their flexibility such as with bandages so as to be readily usable.
It is an object of this disclosure to meet the difficulties encountered in the prior art and to make available both safe and economical actively antimicrobial surface structures and their method of manufacture.
Catheters, implants, bandages, diapers, diaper liners, dressings, and the like can be readily coated with thin films of active elements which, when in contact with body fluids, release substances and ions which stop the growth of or kill various types of microorganisms. As here described, there is no requirement to apply any outside electric current to maintain sustained levels of ion release to treat the infected area.